1. Field
The present disclosure relates to a wireless communication, and more particularly, to a method and apparatus for controlling soft buffer for TDD-FDD carrier aggregation.
2. Discussion of the Background
The wireless communication system may support Frequency Division Duplex (FDD) and Time Division Duplex (TDD). In the FDD, a carrier used for an uplink (UL) transmission and a carrier used for a downlink (DL) transmission exist, respectively, and both the UL transmission and the DL transmission are simultaneously executed in a cell. In the TDD, a UL transmission and a DL transmission are distinguished from each other, based on a time, in a single cell. In the TDD, an identical carrier may be used for a UL transmission and a DL transmission Thus, a base station and a UE repeatedly execute conversions between a transmission mode and a reception mode. The TDD includes a special subframe so as to provide a guard time for converting a mode between transmission and reception. The special subframe may include a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS), as illustrated in the drawings, e.g., FIG. 3. For the TDD, through various UL-DL configurations, resources may be asymmetrically allocated for UL and DL transmissions.
For an effective, reliable communication, a Hybrid Automatic Repeat Request (HARQ) process may be used. Unlike an Automatic Repeat Request (ARQ) process, a Forward Error Correcting Code (FEC) may be used for the HARQ process. For example, if a receiver correctly decodes a data signal (or a packet), the receiver may feedback an acknowledgement (ACK) so as to inform the transmitter that the data signal was correctly decoded. If the receiver fails to correctly decode a data signal, the receiver may feedback a negative acknowledgement to the transmitter to inform the transmitter of the decoding failure of the data signal. A User Equipment (UE) may store a part or entirety of data corresponding to the data signal in a soft buffer of the UE. The UE receives a packet retransmitted from the transmitter, and combines the stored data and the retransmitted data, so as to increase a probability of success of decoding. The UE continuously executes the HARQ process until the packet is correctly decoded or until a predetermined maximum number of retransmissions are executed. Therefore, a space of the soft buffer needs to be reserved for the HARQ process related to a packet that the UE fails to correctly decode. When the soft buffer is fully utilized, or the space is insufficient, the UE may not execute the HARQ process.
Currently, frequency resources are scarce and various technologies are used in a part of the broad frequency bands. For this reason, to satisfy a higher data transmission rate requirement, as a scheme for securing a broadband bandwidth, each scattered band is designed to satisfy basic requirements for operating an independent system and a Carrier Aggregation (CA) has been employed, which binds up a plurality of bands as a single system. A band or a carrier that may independently operate may be defined as a Component Carrier (CC). Further, a TDD-FDD CA supports a CA of an FDD carrier and a TDD carrier. When the TDD-FDD CA system is utilized, it may be required to execute the HARQ processes associated with a plurality of Component Carriers. More specifically, the HARQ processes associated with the TDD and FDD carriers may need to be stored in the soft buffer of the UE. Therefore, when the TDD-FDD CA is configured for the UE, there is a desire for a method of processing or controlling the soft buffer of the UE for the HARQ processes associated with a plurality of CCs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art.